As an exhaust gas filter which traps particulate matter contained in the exhaust gas of an internal combustion engine to prevent the particulate matter from being discharged into the atmosphere continues to trap particulate matter, eventually the trapped particulate matter causes a blockage. In such a case, a regeneration operation must be performed to raise the temperature of the exhaust gas so that the accumulated particulate matter is forcibly burned and removed.
JP2002-364436A, published by the Japan Patent Office in 2002, proposes supplying a catalyst disposed upstream of an exhaust gas filter with unburned hydrocarbon by performing a so-called post-injection, in which additional fuel is injected, during the expansion stroke of an internal combustion engine, and raising the temperature of the filter using heat generated by the catalytic reaction of the unburned hydrocarbon.